Jason Bateman has his shtick and he’s sticking to it. As an actor, he’s cultivated a second act as a deadpan machine dispensing withering sarcasm. It’s a good act, if one he whips out in film after film after film. (A rare exception is “The Gift,” in which he subtly twists his persona to unleash the sociopath lurking underneath.) As a director, he’s equally limited. Like “Bad Words,” “The Family Fang” is a sour joke-fest that takes a mid-film turn for the serious and borderline-maudlin, only to become smaller and, in “Fang”’s case, very nearly risible.

Bateman helmed and stars in (though did not write) “Fang,” in which he and Nicole Kidman play Baxter and Annie, siblings whose only real connection is that both are deeply unhappy. That, and this: They were once an avant-garde version of child stars. As kids, they participated in performance art pieces created by their parents (played in their autumn years by Christopher Walken and Maryann Plunkett), which involved “Punk’d”-like pranks on real people. Their attempts at redefining themselves as adults have been bumpy. Baxter had a hit novel and a poorly received follow-up, with a third held back by crippling writer’s block. Annie became an actress most famous for chucking her clothes and tabloid-y boozing.

A quirky (but genuinely funny) injury winds Baxter in the hospital, which leads to a shotgun family reunion, which their parents — unapologetic about the psychic harm they did to their children — try to turn into a comeback. When their latest piece fails miserably, the elders suddenly go missing and are presumed dead. Baxter and Annie refuse to believe this isn’t simply another stunt, and go about trying to chase a trail of bread crumbs that may or may not exist.

Bateman knows his way around a mordant joke, and both he and Kidman are an enjoyably overcast pair, prone to cynical one-liners and putdowns. Kidman is especially excellent, not falling back on cliches about troubled, sex-happy actresses but playing Annie as damaged but confident about finding herself in middle age. She even reunites with David Lindsay-Abaire, the screenwriter who penned the film of the play “Rabbit Hole,” one of her best roles, here adapting a novel by Kevin Wilson.

This time Lindsay-Abaire doesn’t quite master dragging a source from one medium into another. “Fang” feels novelistic, which is to say its nuances have been flattened out, its flashbacks become quickie distractions, and the only reason its characters aren’t one-note is due to fine performances. As the evil parents, Walken works an arrogance that’s downright sad in old age, while Plunkett makes her character seem like a sweetheart who’s been dragged into sinister doings by a more charismatic partner.

By the time “Fang” has plodded into a twist ending, it’s settled on the belief that some artists — especially performance art types — are just pathetic monsters who don’t care about the harm they do to others in the name of their craft. We say all this knowing that unkind words will once again keep people from seeing yet another fine turn from Kidman. For approximately the millionth time she proves she doesn’t deserve her decade-plus box office poison period, even in the cases, like this, where a fantastic performance is stuck inside a piece that in no way deserves her.